1. Field of the Invention
The present invention relates to the technical field of image processing and, more particularly, to a system for applying multi-direction and multi-slope region detection to image edge enhancement.
2. Description of Related Art
The operations of image edge enhancement and de-noise in image processing are regarded as the oppositely relative filter operations. Namely, if only the image edges are enhanced, the noises cannot be eliminated. Accordingly, the de-noise operation is typically performed before the edge sharpness algorithm is enhanced, so as to avoid erroneously determine the edge transient region caused by the high frequency components of the noises. Conversely, if the de-noise operation followed by the enhancement operation is performed, the algorithm selected for the de-noise operation can indirectly affect the enhancement effect.
The edge enhancement algorithm in the prior art typically uses multiple filters to separate corresponding band regions. However, an obtained output signal requires combining a plurality of determinations and setting the weighting parameters to thereby reach to the desired image quality. As shown in FIG. 1, U.S. Pat. No. 5,414,473 granted to Hong for an “apparatus and method for enhancing transient edge of video signal” has disclosed three filters to perform the edge enhancement in which appropriate correction of the weighting parameters is required for different image requirements. In addition, the sampling rule of the parametered digital filters is limited by the hardware configuration and cannot be modulated dynamically according to the current edge transient length. Such a way can advantage in the image enhancement to have the higher continuity, but the obtained result has a lower direct meaning, i.e., the parameters are determined after the long-running tests. Since the weighting parameters of the filters are changed with the different practical designs, they are manually adjusted as needs in the practical images corresponding to the different designs. The hardware implementation becomes heavy and complicated when the number and length of filters increases, which further increases the cost and easily skips the fine lines even the anti-aliasing is better.
U.S. Pat. No. 6,094,205 granted to Jaspers for a “Sharpness control” has disclosed the uses of second derivative to detect the edge transient regions, and the first derivative and the contour filter to adjust the gain of the edge enhancement, with the help of the maximum and minimum detection. As shown in FIG. 2, when such a method is applied in a digital signal, the cooperation of all the devices is required, which increases the hardware complexity on, for example, searching the pixels for the maximum and the minimum ones. In addition, a wrong determination appears in using the filter to find the high frequency regions (edge transient regions) for it is easily affected by the noise interference or the fine lines. Since the output of a digital filter is referred as a determinant of the gain for the edge enhancement, the sampling rule of the digital filter can be restricted by the hardware. Therefore, the image quality obtained from lower bandwidth and larger edge regions is not increased apparently. Accordingly, when the same algorithm is applied to process a lower-bandwidth image, a larger change in the prior hardware configuration is required, and the hardware requirement is relatively increased. Further, the gain adjusted by the filter can have an unexpected change due to the noise interference, especially at the enhanced edge transient regions, where the unexpectedness of luminance/chrominance/RGB changes is more serious.
Therefore, it is desirable to provide an improved system to mitigate and/or obviate the aforementioned problems.